Fuel contaminants such as sulfur, chlorine, vanadium, and others present major regulatory and refinery process burdens for crude oils and heavy fuels, and there are currently no adequate on-line analyzers to measure these contaminants. This disclosure relates to a real-time, on-line sample flow and analysis system for contaminant monitoring in crude oils and other heavy fuels, for refining applications. By measuring these contaminants real-time, fuel refineries will benefit from extended overall uptime, increased process efficiency, and improved safety.
The presence of trace levels of contaminants in petroleum feedstocks is a growing problem in petroleum refining. Sulfur is a common component in crude oil streams—and its removal from final product is mandated due to its impact on the environment, as regulated by the US EPA under the Clean Air Act. Sulfur is harmful to the environment, and the cost of its removal is high. Therefore, monitoring sulfur levels early in the refining process is important.
Chlorine and vanadium contaminants are considered “bad actors” by the refining industry for primarily non-regulatory, process control reasons. In a 2004 industry white paper produced by the Crude Oil Quality Group, these contaminants were included in a group of eight contaminants of most concern to the industry.
Chlorides pose one of the greatest problems to the refining industry. According to a 2005 paper by The National Association of Corrosion Engineers (“NACE”): “Recently, an increasing number of refineries have experienced extreme corrosion and fouling in crude distillation unit overheads and/or naphtha hydrotreating units. The root causes were traced to severe spikes in the chloride levels.”
Most chloride salts in crude oil are inorganic (sodium, magnesium, or calcium chloride) and can be effectively removed by a desalter. The nonextractable chlorides are not removed in the desalter, and can break down from downstream heating and processing to form hydrochloric acid, causing corrosion and fouling problems. The 2005 NACE paper documented over 20 cases of chloride damage to production facilities. It has also been reported that the chlorides collect in certain confined areas of various refinery systems, therefore multiplying their corrosive affects, even if the input levels are low. The NACE report also stated the extent to which refiners must monitor this problem: “Some companies called for [a maximum of] 5 ppm, while others called for 0 ppm organic chlorides. Typically, most companies called for from 1 to 3 ppm. From a corrosion point of view, the upper limit of 3 ppm is too high—a more realistic limit is 1 ppm . . . . Other companies flatly reject any and all crude oils containing organic chlorides in any amount.” (NACE International Publication 34105)
Because chlorides are problematic, refiners may actually preclude the use of certain feedstocks due to the risk of unknown chloride levels. And, as the world's more desirable sources of crude oil are depleted, less pure crude is becoming more common. These sources are likely to have more salts, or higher sulfur content, that will require monitoring.
Chlorides may not only be naturally introduced, but also may arise from process sources. These sources include: chemicals used in enhanced oil recovery processes; chlorinated solvents used in crude oil production, transportation and storage; chlorinated additives used in production, transportation, and storage (possibilities include wax crystal modifiers, biocides, corrosion inhibitors, flocculation additives, and emulsion breakers); and/or the mixing of crude oil byproducts (slop) or other materials with new crude for purchase on the open market as a way to (illegally) boost sales and dispose of waste.
While most of these sources of chloride contamination are outside the control of the refinery, they all have implications for the refinery process at the input, process, and output stages.
In another challenge, the element Vanadium deactivates cracking catalysts. Also, when products containing vanadium are burned, corrosion of turbine blades may occur. According to the Crude Oil Quality group, off-specification coke may be produced when levels of vanadium are too high in crude oil.
Technical Challenge—Sample Handling For On-Line Measurement of Crude and Heavier Fuels:
Any proposed on-line measurement techniques for low level contaminants in upstream crude flows, or other heavy fuels in this industry, must confront certain technical challenges.
Common trace analysis methods include chemical techniques such as titration, ion and gas chromatography, microcoulometry, and combustion spectroscopy. There are limitations to these methods. The first limitation is the low limit of quantification (LOQ) necessary. Process control in the petroleum industry may call for a LOQ of 0.5 ppm or less for chlorine. None of these methods provides a LOQ below 1 ppm except microcoulometry, but microcoulometry requires frequent calibration and cumbersome maintenance, and is a difficult method to use. Another limitation is that most of these techniques are laboratory-based methods and cannot be applied to online measurement due to complicated sample preparation and handling requirements. Finally, some of these methods may not measure all chlorides in a sample (e.g., gas chromatography).
Another major challenge is that most of these heavy upstream flows are “dirty” in an analytical sense, with viscosities not amenable to smooth flows through an analyzer. To accurately measure these contaminants online, consistent sample flows are necessary over a range of viscosities.